In recent years, a hybrid electric vehicle (HEV) including an electric motor and an internal combustion engine has been put to practical use. In addition, an electric vehicle (EV) including an electric motor has also been put to practical use.
A wireless power supply device, which performs wireless power supply to the electric vehicle or the like, magnetically couples a primary coil of a power supply side with a secondary coil of a power receiving side to transmit electric power from the power supply side to the power receiving side in a wireless manner.
Such a wireless power supply device is disclosed in, e.g., Patent Literatures 1 and 2.
In a wireless power supply device of Patent Literature 1, axes of a primary coil and a secondary coil are vertical and coaxial. This type of wireless power supply device is called “a circular type”.
Additionally, in a wireless power supply device of Patent Literature 2, axes of a primary coil and a secondary coil are positioned in parallel with each other. This type of wireless power supply device is called “a solenoid type”.
The wireless power supply is roughly classified into three systems of an electromagnetic induction system, an electric wave system, and a magnetic field resonance system.
The electromagnetic induction system uses electromagnetic induction in which, when an electric current flows through one of two adjacent coils, a magnetic flux is generated as a medium to generate an electromotive force in the other coil.
In the electric wave system, a current is converted into an electromagnetic wave, which is transmitted and received via antennae.
In the magnetic field resonance system, a magnetic flux is used as a medium in the same manner as in the electromagnetic induction system, but a resonance phenomenon of an electric circuit is positively utilized, and an induction current flowing through a coil is amplified.
In the abovementioned wireless power supply device, when a metal foreign matter enters space between the primary coil and the secondary coil, there is a possibility that an eddy current is generated in the metal foreign matter and the metal foreign matter heats by Joule heat.
Therefore, a wireless power supply device which detects such a foreign matter is disclosed in, e.g., Patent Literature 3.
In the wireless power supply device of Patent Literature 3, which is a wireless power supply device of the abovementioned electromagnetic induction system, a third coil is interposed between a first coil and a second coil, and a foreign matter between the first coil and the second coil is detected on the basis of an induced voltage generated in the third coil.